Electrochemical deposition of active material into the pores or interstices of a foraminous electrode support is an alternate to chemical or mechanical deposition of such material and, at least in some instances, may be preferred. For example, in the formation of the positive (nickel) electrode for a nickel-cadmium cell, the nickel is applied to the electrode as a nitrate and then, after impregnation, converted to the desired hydroxide by treatment with caustic. The resultant electrode is not too densely packed resulting in a charge to volume ratio which is lower than desirable for a high capacity cell of minimum volume.
Electrodeposition of the nickel material using the conventional constant current deposition techniques common to the art results in the direct formation, in the electrode, of a hydrated form of nickel-hydroxide which is then dehydrated by treatment with caustic.
This technique has not met with wide spread acceptance, however. One of its drawbacks is the formation or deposition of undesirable surface depositions which add to the overall weight of the electrode, impede further internal deposition, and lastly interfere with subsequent use of the electrode in a cell by flaking off and shorting the cell as the material is converted from its reduced form to its oxidized form.
The use of additives such as, for example, cobalt, in the active material of the electrode to inhibit fading of the electrode is also well known. However, maintaining the correct ratio of cobalt to nickel in an electrochemical impregnation, unlike a batch process, present additional difficulties.